1. Field of Invention
This invention relates to automatic fixed speed driving systems and in particular to releasing means for such automatic fixed speed driving systems.
2. Prior Art
Automatic fixed speed driving systems are known in the art as a means for automatically controlling the driving speed of a motor vehicle at a constant rate without stepping on the accelerator once the speed is fixed at a certain speed at the driver's option. Such systems are able to reduce the driver's fatigue and to increase the gas mileage of the motor vehicle when it is cruising continuously at a fixed speed along the highway, etc. There have been several forms of automatic fixed speed driving systems but the basic composition is such that a comparison between the voltage drive from a driving speed and a voltage from a memory value from a memory circuit set by a speed command signal is utilized to generate a speed command signal by which the carburetor is controlled to speed up or slow down by means of an actuator provided on the carburetor.
A typical conventional type of automatic fixed speed driving system automatically starts to operate when a set signal is provided to a control circuit or the driving speed reaches the previously set speed. The automatic fixed speed driving system is released when the control circuit receives a releasing signal. Typically the releasing signal is supplied to a releasing device by way of braking action and is detected as an electrical signal by the on and off action of the stop lamp circuit. Since if one is driving a motor vehicle with a blown fuse in the stop lamp circuit a releasing signal is not generated, the prior art devices create a particular danger to the operator of such a motor vehicle.
To overcome such a problem, a system equipped with a transistorized detection circuit which detects a blown stop lamp fuse has been developed. Such a system typically has another drawback in that the automatic fixed speed driving system is always released when the stop lamp fuse blows even if the motor vehicle is at the pre-set cruising speed and the driver does not apply the brake. Furthermore there is an added disadvantage in that the transistorized detection circuit continually draws current and therefore consumes power from the battery even when the ignition switch is in the off state.